Hi,
For a personal project I had to find a way to make a PWM signal with a fixed period/frequency to control a Solid State Relay that modulate resistive load on 50Hz 230v AC. I've made an article on my github to explain how I configure an ATmega328P to produce a 2.5Hz PWM signal that is used for a PID control of a heating element. The code of this project is also available on my github, if it can help it will be great.
I don't know if it is the good way to share my feedback with the community but the links are below: